CT colonography detects 85% of large polyps in patients at increased risk of colon cancer

Clinical Question

How accurate is computed tomographic colonography for the detection of advanced neoplasia in patients at increased risk of colorectal cancer?

Bottom Line

Computed tomographic (CT) colonography will detect approximately 85% of large polyps and adenocarcinomas in individuals at increased risk of colorectal cancer (CRC), including those with positive family history in a first-degree relative, personal history of adenoma, or positive fecal occult blood test (FOBT) result. Because of the increased prevalence of advanced neoplastic disease in this at-risk population, the negative predictive value of the test (96.3% overall; 84.9% in the FOBT-positive group) may limit patient and clinician acceptance. Overall, approximately 1 in 25 advanced lesions remained undetected, with approximately 1 in 7 similar lesions remaining undetected in individuals with a positive FOBT result. (LOE = 1b)

Reference

Regge D, Laudi C, Galatola G, et al. Diagnostic accuracy of computed tomographic colonography for the detection of advanced neoplasia in individuals at increased risk of colorectal cancer. JAMA 2009;301(23):2453-2461.  [PMID:19531785]

Study Design

Cohort (prospective)

Funding

Government

Setting

Outpatient (specialty)

Synopsis

The accuracy of CT colonography in individuals at increased risk of CRC is unknown. These investigators recruited 937 adults, aged 18 to 70 years, at increased risk of CRC because of either family history of advanced colorectal neoplasia in a first-degree relative (39.8%), personal history of adenomas (36.6%), or positive results from FOBTs (23.6%). All patients were free of significant bowel symptoms. After a standard bowel preparation, each participant underwent CT colonography followed by colonoscopy on the same day in the same medical center. One radiologist interpreted the CT colonography and reported the findings separately for 6 bowel segments. Endoscopists masked to the results of the CT colonography performed the colonoscopy at least 3 hours later. At the end of each bowel segment evaluation by endoscopy, CT colonography results were disclosed. If a polyp measuring 6 mm or larger was initially detected at CT colonography and not seen on colonoscopy, the segment was carefully re-examined to resolve the discrepancy. Pathologists evaluated and classified all biopsy specimens using standard World Health Organization criteria. Adenomas 10 mm or larger, with more than 20% villous component, or with high-grade dysplasia were considered advanced. The prevalence of advanced lesions in patients in the family history group, personal history of adenoma group, and FOBT positive group was 7.5%, 11.1%, and 50.2%, respectively. The sensitivity of the CT colonography for the detection of at least 1 advanced lesion 6 mm or larger was 85.3%. CT colonography was 87.8% specific in correctly classifying results as negative. The overall negative predictive value (the percent of negative tests that are truly negative) was 96.3%, meaning that approximately 1 in 25 advanced lesions remained undetected. The negative predictive value in the FOBT-positive group was 84.9%; that is, approximately 1 in 7 advanced lesions remained undetected.